Protestors after the death of Michael Brown. (Photo: Light Brigading/Flickr)

The recent, well-publicized shootings of unarmed black men by police officers have raised many troubling questions. Perhaps the most fundamental: whether these tragedies reflect a larger societal bias that sees men of color as threatening figures, which could in turn prompt even well-trained police officers to adopt a shoot-first-ask-questions-later mindset.

Over the past decade, many studies have attempted to prove or disprove the existence of such prejudice; the results have been mixed and sometimes contradictory. But in a newly published analysis of 42 such studies, University of Illinois psychologists Yara Mekawi and Konrad Bresin conclude that, unfortunately, this racial bias is indeed quite real.

"Compared to white targets, participants were quicker to shoot armed black targets, slower to not shoot unarmed black targets, and were more likely to have a liberal shooting threshold for black targets," the researchers write in the Journal of Experimental Social Psychology.

The false alarm rate, in which black subjects who were not carrying guns were inadvertently shot, was higher in states with more permissive gun laws.

These key results, they add, were found "across all studies," whatever their other differences.

The studies the researchers looked at were usually conducted in laboratory settings. In total, just over two-thirds of the participants were white; men and women were equally represented. Typically, participants were "shown images of black and white targets holding either a gun or a neutral object (such as a cell phone) and given less than one second to respond whether they should 'shoot' or 'not shoot' the target."

The average effect across the studies showed a significant bias against black targets. But there was little agreement on the underlying cause (or causes) to this bias—an essential piece of information if better training regimens are to be developed, and effective interventions implemented.

Deconstructing the results, Mekawi and Bresin observed consistent, significant effects for two variables: the shooter's reaction time, and his or her "shooting threshold biases."

"Participants may be faster to shoot black (vs. white) targets with a gun because it fits with a racial stereotype," they write. "People respond to stereotype-consistent information more quickly than stereotype-inconsistent information."

Supporting this notion, they discovered a correlation between that tendency and the endorsement of stereotypes. "However, this relation was quite small," they write, "suggesting other factors may be at play."

That led the researchers to suspect that "shooting threshold"—an individual's underlying proclivity to shoot, or not shoot, at a potentially dangerous figure—may be a stronger factor. They found participants in the studies displayed a greater bias toward taking action—that is, pulling the trigger—when the target was black rather than white.

This bias was greater in "states with more permissive gun laws," they report. The false alarm rate, in which black subjects who were not carrying guns were inadvertently shot, was also higher in such states.

While it's impossible to know precisely why, the researchers speculate that residents of these states "are more willing to use guns against perpetrators of crime, who they assume, due to stereotypes, to be racial and ethnic minorities," Mekawi and Bresinwrite. "Thus it is possible there are cumulative effects of permissive gun laws, willingness to shoot, and race-related fear of crime that, together, contribute to racial shooter bias."

As such speculation suggests, we're a long way from understanding precisely what is driving this prejudicial behavior, or how to counteract it. But the researchers argue further work on this topic "should be a priority to researchers interested in social justice."

At the very least, anyone handling a gun in a potentially threatening situation—police officer or civilian—needs to understand that our instinctual urge to pull the trigger may be based on nothing more than unconscious racial bias.

Findings is a daily column by Pacific Standard staff writer Tom Jacobs, who scours the psychological-research journals to discover new insights into human behavior, ranging from the origins of our political beliefs to the cultivation of creativity.